Reverse osmosis is a phenomenon that was first considered in the 1950's as a method for separating the components of a solution. Since that time the process has been highly developed and refined and is now one of the primary methods of producing desalinated water from saline water.
In the reverse osmosis process the solution to be separated is passed under high pressure past a reverse osmosis membrane enclosed within a higher pressure chamber. The reverse osmosis membrane allows a certain percentage of the solution to pass through the membrane as potable water, while rejecting the various impurities within the water, including salt.
Although reverse osmosis can be used for many sorts of separation it is most commonly used for desalination of salt or brackish water, especially sea water. Accordingly, for convenience, throughout this specification the feed stock or saline water to be desalinated will be described generally as “feed water” the desalinated water produced as “product water” and the feed water which has had the product water extracted from it, as “brine” and reverse osmosis as “RO”.
In a conventional RO system, from 10% to 40% of the feed water is recovered as potable water, but regardless of the recovery rate, 100% of the feed water passing through the system must be brought to operating pressure by the high pressure pump. To bring the feed water to the necessary pressures required for the RO operation, conventional systems require significant amounts of energy. Various ways have been explored to reduce the energy required.
Among the ways that have been tried are energy recovery methods but if energy is being recovered, then more energy than needed is being supplied. Furthermore, these methods are unable to recover all the energy being lost by conventional methods.
Disclosed in U.S. Pat. No. 5,462,414 is a pump employed in reverse osmosis systems. The pump is a dual chamber pump, each chamber having a piston with the pistons linearly reciprocated alternatively pumping feed water towards the reverse osmosis membrane of the desalination system.
The ram and piston assembly is caused to move by the supply of feed water to one end of the hydraulic unit. The forward movement of the ram at this end causes the ram and piston at the other end to move at the time and at the same rate. Feed water at this end is contained within a closed loop either side of the piston, said closed loop also includes a RO membrane.
As the piston moves feed water is driven from one side of the piston to the other via the RO membrane. As the feed water enters the side of the piston containing the ram, the pressure of the water is intensified by the volume of the ram. This intensified pressure of the feed water causes the RO process to take place.
This device is far superior to those that had preceded it but still has drawbacks in that it has a large number of parts and a fixed recovery rate, making it unfit to alter the volume recovery rate. It is also unsuitable to be retro fitted to existing systems.
Disclosed in U.S. Pat. No. 6,491,813 are two pumps similar to that as described in U.S. Pat. No. 5,462,414. The first solution offered in this patent, is the same as the above. The second solution provides for pressure intensification by the use of a high pressure pump. This system still has its drawbacks due to a large number of parts and the use of non return valves.